Seasonal snowfall for 1981–2010 averaged 10.8 inches (27.4 cm) Olympia averages 50 inches (1,270 mm) of precipitation annually and has a year-round average of 75% cloud cover.Annual precipitation has ranged from 29.92 in (760 mm) in 1952 to 66.71 in (1,694 mm) in 1950; for water year (October 1 – September 30) precipitation, the range is 32.71 in (831 mm) in 2000–01 to 72.57 in (1,843 mm) in 1998–99.
Most of western Washington's weather is brought in by weather systems that form near the Aleutian Islands in Alaska.
The Deschutes River estuary was dammed in 1951 to create Capitol Lake.
Much of the lower area of downtown Olympia sits on reclaimed land. The region surrounding Olympia has a warm-summer Mediterranean climate (Köppen Csb), whereas the local microclimate has dry summers and cool July and August overnight lows.
In 1846, Edmund Sylvester and Levi Smith jointly claimed the land that now comprises downtown Olympia. Its population steadily expanded from Oregon Trail immigrants.
In 1850, the town settled on the name Olympia, at the suggestion of local resident Colonel Isaac N.